Depinning, Melting and Sliding of Generalized Wigner Crystals in Moire Systems

TL;DR

This paper numerically investigates the depinning, sliding, and melting behaviors of generalized Wigner crystals in moire heterostructures, revealing complex dynamics and phase transitions influenced by temperature, filling factors, and external drives.

Contribution

It provides new insights into the depinning and sliding mechanisms of Wigner crystals in moire systems, including two-step depinning and asymmetric transport phenomena.

Findings

Depinning threshold varies with filling and temperature.

Sliding states include moving fluids and crystals.

Transport asymmetry arises from interstitial and hole dynamics.

Abstract

We numerically examine the depinning, sliding, and melting of commensurate and incommensurate Wigner crystals on two-dimensional hexagonal periodic substrates near fillings of 1/3, 1/2, and 2/3 to model the dynamics of generalized Wigner crystals in moire heterostructures. At low temperatures where thermal fluctuations are irrelevant, for commensurate fillings we find a strongly pinned state that depins into a sliding crystal, while at incommensurate fillings, the depinning threshold is strongly reduced. For fillings below 1/2, the depinning occurs in a two-step process. Above the first depinning threshold, there is an extended range of drives where the conduction occurs via the sliding of anti-kinks along the charge stripes, followed by a second threshold where all of the charges begin to slide. At finite temperatures, the external driving reduces the effective melting temperature at commensurate fillings and enhances creep at incommensurate fillings. We show that depinning into different sliding states, such as moving fluids or moving crystals, produces nonlinear features in the transport curves. We also show that transport is asymmetric on either side of a commensurate filling due to the different dynamics for interstitials versus holes in the commensurate structure. A variety of sliding states should be accessible for generalized Wigner crystals at finite temperatures even for low drives. If experiments can realize sliding dynamics in moire systems, it would open a new class of commensurate and incommensurate phases for study. Additionally, the sliding dynamics and anti-kink flow could provide new functionalities for charge transport in moire heterostructures.